Method and apparatus for detecting presence of an unmodulated RF carrier prior to a communication frame

ABSTRACT

A measurement signal, the measurement signal indicative of a bias in a signal received via a communication channel, is generated. A detection signal, the detection signal indicative of presence of an unmodulated radio frequency (RF) carrier prior to a communication frame in the signal received via the communication channel, is generated using the measurement signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This present application is a continuation application of U.S.application Ser. No. 11/213,907, now U.S. Pat. No. 8,032,095, entitled“METHOD AND APPARATUS FOR DETECTING CARRIER LEAKAGE IN A WIRELESS ORSIMILAR SYSTEM,” filed on Aug. 30, 2005, the disclosure of which isexpressly incorporated by reference herein in its entirety, which claimsthe benefit of U.S. Provisional Application No. 60/658,334, filed onMar. 3, 2005, the disclosure of which is expressly incorporated byreference herein in its entirety.

BACKGROUND

1. Field of the Disclosure

The disclosure is directed generally to a method and apparatus thatdetects wireless transmission problems and, more particularly, todetecting an unmodulated radio frequency (RF) carrier prior to acommunication frame in a signal received via a communication channel.Moreover, the disclosure is directed to a method and device to receiveand/or recover a transmission frame in the presence of an unmodulatedradio frequency (RF) carrier prior to the communication frame.

2. Related Art

In order to transmit data in a transmission frame in a wireless systemfrom a transmitter to a receiver, including a wireless network, thetransmitter must first turn on or power up a power amplifier and/orother related components. Normally the power up process takes about twoto three micro-seconds for a power amplifier, and its associatedcircuitry, to fully power up in order to transmit a transmission frame.During the period of time that the power amplifier is powering up, notransmission of a transmission frame with data takes place. This is donein order to minimize any signal distortion caused by powering up theamplifier. However, the wireless system transmitter may transmit duringthe power up time period an unmodulated radio frequency carrier prior tothe transmission of the transmission frame. The power of thisunmodulated radio frequency carrier or carrier leakage in thetransmission frame is typically about 20 to 30 dB below the actualsignal power of the remaining part of the transmission frame. Moreover,the carrier leakage may have an almost near DC characteristic in thatthe signal is mostly ones or zeros.

FIG. 1 shows an exemplary transmission frame 100 having carrier leakage110 in the front portion of the transmission frame 100. In particular,the desired portion of the transmission frame 100 that is to be receivedin a receiver is the preamble 120, header/signal field 140, and data 160(payload). It is not desired for a receiver to receive any carrierleakage 110. In this regard, the undesired reception of the carrierleakage 110 is generally minimal when there is a large distance betweenthe transmitter and the receiver. Accordingly, desired signal strengthcan be still be above the receiver sensitivity level whereas the carrierleakage 110 is then buried in thermal noise and the carrier leakage 110has little or no effect. Moreover, the reduced power of the carrierleakage 110 (specified at about 20-30 dB below the actual signal power)allows the receiver to be able to avoid receiving this undesired signalin the background.

Carrier leakage is more problematic when the transmitter and receiverare relatively close, such as in current Wireless Local Area Networks(WLAN) systems, for example those compliant with IEEE 802.11, 802.11(a),802.11(b), 802.11(g), 802.11(n), 802.16, and 802.20, which are beingused with increasing frequency in relatively close quarters in homes,businesses, and commercial applications. When the transmitter and thereceiver are relatively close, the receiver has a tendency to falselystart receiver processing in response to the carrier leakage 110. Inparticular, the nearer the receiver to the transmitter and the shorterduration of the energy at an antenna can potentially or falsely startreceiver processing, gain control, signal detection, and/orsynchronization mechanisms and the like. For example, in some WLANsystems, such as IEEE 802.11(a), the initial symbol timingsynchronization relies on certain periodicity of a short preamble. Sincethe unmodulated radio frequency carrier, including the carrier leakage110, is near DC at a base band, this fulfills the periodicityrequirement and subsequently causes the receiver to faultily trigger andstart detection of the transmission frame 100 together with the carrierleakage 110. Since the carrier leakage 110 is much lower in powercompared to the actual transmission frame 100 parts including thepreamble 120 of the signal, the header/signal field 140, and data 160,when the gain control locks on to the carrier leakage 110, the remainingpart of the transmission frame 100 including parts 120, 140, 160 may besaturated in the transmitter and lost once received in receiver. Thiswould subsequently cause a significant degradation in the throughputperformance that has been both observed in real operation andenvironments in the lab, as well as in simulations.

SUMMARY OF THE DISCLOSURE

In an embodiment, an apparatus comprises a measurement circuitconfigured to generate a measurement signal indicative of a bias in asignal received via a communication channel, and a circuit configured togenerate, using the measurement signal, a detection signal thatindicates presence of an unmodulated radio frequency (RF) carrier priorto a communication frame in the signal received via the communicationchannel.

In another embodiment, a method includes generating a measurement signalindicative of a bias in a signal received via a communication channel,and generating, using the measurement signal, a detection signal thatindicates presence of an unmodulated radio frequency (RF) carrier priorto a communication frame in the signal received via the communicationchannel.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the detailed description serve to explain the principlesof the invention. No attempt is made to show structural details of theinvention in more detail than may be necessary for a fundamentalunderstanding of the invention and the various ways in which it may bepracticed. In the drawings:

FIG. 1 shows a typical transmission frame with a transmission havingcarrier leakage;

FIG. 2 shows a single input single output (SISO) receiver andtransmitter system that may use the carrier leakage detection circuitsof the invention;

FIG. 3 shows a circuit for detecting carrier leakage in a SISOtransceiver constructed according to the principles of the invention;

FIG. 4 shows a more detailed embodiment of the circuit for detectingcarrier leakage shown in FIG. 3;

FIG. 5 shows a multiple input multiple output (MIMO) receiver andtransmitter system that may use the carrier leakage detection circuitsof the invention;

FIG. 6 shows a circuit for detecting carrier leakage in a MIMOtransceiver constructed according to the principles of the invention;

FIG. 7 shows a more detailed embodiment of the circuit for detectingcarrier leakage shown in FIG. 6, including a sensitivity selector;

FIG. 8 shows a circuit for detecting carrier leakage similar to FIG. 7,but without a sensitivity selector;

FIG. 9 shows a circuit that may be used with the carrier leakagedetection circuits of the invention for operating with a plurality oftransmission protocols;

FIG. 10 shows a flow chart of a process for detecting carrier leakagethat may be implemented in the circuits of the invention; and

FIGS. 11, 12, 13, 14, and 15 show various exemplary implementations ofthe invention.

DETAILED DESCRIPTION

The embodiments of the invention and the various features andadvantageous details thereof are explained more fully with reference tothe non-limiting embodiments and examples that are described and/orillustrated in the accompanying drawings and detailed in the followingdescription. It should be noted that the features illustrated in thedrawings are not necessarily drawn to scale, and features of oneembodiment may be employed with other embodiments as the skilled artisanwould recognize, even if not explicitly stated herein. Descriptions ofwell-known components and processing techniques may be omitted so as tonot unnecessarily obscure the embodiments of the invention. The examplesused herein are intended merely to facilitate an understanding of waysin which the invention may be practiced and to further enable those ofskill in the art to practice the embodiments of the invention.Accordingly, the examples and embodiments herein should not be construedas limiting the scope of the invention, which is defined solely by theappended claims and applicable law. Moreover, it is noted that likereference numerals represent similar parts throughout the several viewsof the drawings.

FIG. 2 schematically shows how the invention may be implemented in awireless single input single output (SISO) receiver and transmittersystem 600. In particular, the wireless system 600 includes atransmitter 610 that transmits a transmission frame 100 to a receiver620. Of course, it should be apparent that the transmitter 610 can alsoinclude a receiver (transceiver) and the receiver 620 can include atransmitter (transceiver). The receiver 620 shown in FIG. 2 furtherincludes a carrier leak detector circuit of the invention. Accordingly,the receiver 620 is able to detect carrier leakage 110, controlreception based thereon, and operate with greater throughput.

FIG. 3 shows a circuit for detecting carrier leakage in a SISOtransceiver such as a SISO system 600. In particular, the receivedtransmission frame 100 is received initially in a receiver and acharacteristic of the signal, such as the logical states thereof, isstored in the buffer 510. The logical states contemplated for use in theinvention may be any logical states known in the art, includingpolarity, logical ones and zeros, and similar states. For ease ofexplanation, the detailed description will reference ones and zeros asthe exemplary logical states, but any such known logical state may beemployed in the invention. As described herein, in order to determinewhether the characteristic of the signal stored in the buffer has aparticular bias in favor of a logical state, the circuits of theinvention either count the number of a particular logical state, suchones or zeros, in the stored signal, the number of the transitionsbetween logical state in the stored signal, or the time period in whicha particular logical state is resident in the signal. Once the logicalstate is counted or timed in a bias detector of the invention, a biasevaluator determines whether the signal has a particular bias in favorof one of the logical states by comparing the values to one or morepredetermined thresholds. The invention uses this bias information todetect a carrier leakage, which carrier leakage 110 does not typicallyhave an equal number of logical states. On the contrary, carrier leakagetypically has a predominant number of one state. Accordingly, detectinga bias for a window or portion of a signal allows detection of thecarrier leakage.

The buffer 510 holds the characteristics of the received signal within awindow of time. The size of window may be controlled based on a windowsize input 550. The window size input 550 may be set by various featuressuch as the transmission protocol type or may be adaptive to the variousother transmission factors in order to increase throughput. The valuesstored in the buffer 510 are output as an in-phase and quadrature-phasesignal that is input to a bias detector 520 that detects a bias in thesignal output from the buffer 510 from the in-phase and quadrature-phaseoutputs. The bias detector may employ a counter, such as described inthe FIG. 4 embodiment, to determine the quantity of a signal polarity,or logical states, such as ones or zeros, present in a signal with theamount of any of these signal components indicating a bias.Alternatively, a timer may be employed to measure in a time window thelength of time a signal polarity, or logical state, such as ones orzeros, are resident (present) in a signal. In another embodiment, thebias may be detected based on the number of transitions from one stateto another state. Detecting the number of transitions from one state toanother allows the detection of a bias. The amount of bias is thenoutput by bias detector 520 to bias evaluators 530 and 540, which may becomparator circuits, such as described in the FIG. 4 embodiment.

The output of the bias evaluator circuits 530 and 540 determine whetheror not the bias has met a minimum threshold or failed to meet a maximumthreshold (i.e., has allowable transmission signal values). Inparticular, if the bias exceeds a maximum threshold or is less thanminimum threshold, a signal indicating carrier leakage is set and outputfrom the bias evaluator 530 and/or 540. The outputs of the biasevaluators 530 and 540 are input to a control circuit 501 that outputs aleakage detection signal based on at least a logical combination of theoutput of bias evaluators 530 and 540. The signal subsequently is usedat least in part to disable the receiver to avoid a reception error andreduced throughput.

FIG. 4 shows a more detailed embodiment of the FIG. 3 circuit for thedetection of carrier leakage 110 in a SISO type receiver. In particular,the received transmission frame 100 is received initially in a receiverand the signal characteristics, such as the polarities, are stored in abuffer 510, such as a short sync buffer, as ones (or alternativelyzeros) based on input 599. The window time may be responsive to a windowtime signal 550. The buffer 510 holds the polarities of the receivedsignal within the window of time. The values stored in the buffer 510are output as an in-phase and quadrature-phase signal that is input to acounter 520 that counts the number of ones that are output from thebuffer 510 from the in-phase and quadrature-phase outputs within a giventime period. The counter value provides an indication of whether thesamples that are currently being received are part of WLAN shortpreamble or near-DC leakage. If it is a short preamble, the number ofones and zeros would be roughly the same since the signal fluctuatesabout DC. However, if it is a strong near-DC leakage, buffered sign bitswould be mostly ones or mostly zeros depending on the polarity. Once thenumber of ones has been counted in counter 520, the counter 520 outputsthe number of ones to comparator circuits 530 and 540, respectively.

In a specific embodiment shown in FIG. 4, the buffer 510 holds thepolarities of the received signal within a 1.6 microsecond window thatis associated with a particular sampling rate of 40 MHz. Accordinglythere are 64 such stored polarities within the 1.6 microsecond window.

As noted herein, carrier leakage 100 does not typically have an equalnumber of ones and zeros. On the contrary, a carrier leakage typicallyhas a predominant number of zeros or a predominant number of ones.Accordingly, counting the number of ones for a window or portion of asignal allows detection of the carrier leakage. The comparator circuits530 and 540 determine whether or not the number of ones and/or thenumber of zeros has met a minimum threshold or failed to meet a maximumthreshold. Thus, the output of comparator circuits 530 and 540 is basedon whether or not the number of ones (or the number of zeros) has met aminimum threshold or failed to meet a maximum threshold (i.e., hasallowable transmission signal values). In particular, when the number ofones exceeds a maximum threshold (SS_leak_TH) or is less than windowsize minus the maximum threshold (for example 64 minus the maximumthreshold SS_leak_TH (minimum threshold)), a carrier leakage signal isset and output from the comparator circuit 530 and/or comparator circuit540. The outputs of the comparator circuit 530 and the comparatorcircuit 540 are input to an OR gate 550 in control circuit 501.

The OR gate 550 outputs the carrier leakage detection signal when thecarrier leakage detection signal is received from either the comparatorcircuit 530 or the comparator circuit 540. Thereafter the OR gate 550inputs the carrier leakage detection signal to an AND gate 580. The ANDgate 580 ANDs the carrier leakage detection signal together with asignal detection signal (!sigDet). The signal detection signal goes highwhen the receiver has received a valid Clear Channel Assessment (CCA)signal. So when the carrier leakage signal is high and the valid CCAreceived signal is high, the AND gate 580 outputs a leakage detectionsignal. The signal subsequently disables the receiver to avoid atransmission error and reduced throughput.

FIG. 5 schematically shows how the invention may be implemented in awireless Multiple Input Multiple Output (MIMO) receiver and transmittersystem 800. In particular, the wireless system 800 includes at least atransmitter 610 that transmits a transmission frame 100 to a receiver620, and a transmitter 610 n that transmits a transmission frame 100 nto a receiver 620 n. Of course, it should be apparent that thetransmitters 610, 610 n can also include receivers (transceivers) andthe receivers 620, 620 n may include also transmitters (transceivers).In addition, there may be more than two transmitters and/or more thantwo receivers. The receivers 620, 620 n shown in FIG. 5 further includea carrier leak detector circuit of the invention. Accordingly, thereceivers 620, 620 n are able to detect carrier leakage 110, controlreception based thereon, and operate with greater throughput.

FIG. 6 shows a circuit for the detection of carrier leakage 110 in aMIMO transceiver, such as MIMO system 800. The characteristics of aninput 299 of the transmission frame 100 are stored in a buffer 210 aslogical states in the same manner as described above in connection withthe SISO embodiments. The buffer 210 holds the logical states of thereceived transmission frame 100 within a limited time window that isassociated with a particular sampling rate, with the window of timebeing adjustable responsive to an input 250. The values stored in thebuffer 210 are output as an in-phase (I) signal and a quadrature-phase(Q) signal that are input to bias detector 220. The bias detector 220detects the bias in the in-phase and quadrature-phase inputs within agiven time-period in a manner similar to that described in connectionwith the FIG. 3 bias detector 520. Once the bias is detected, the biasis output to bias evaluators 230 and 240, which may be comparatorcircuits as described in the FIGS. 7 and 8 embodiments.

The I and Q phases are 90 degrees offset from one another. The 90-degreeseparation allows for two distinct windows in which the bias isdetected. However, it is contemplated that a single-phase system couldbe used, however it may not be as robust as the I and Q phases but mayrequire less circuit or chip area.

The bias evaluators 230 and 240 determine whether or not a bias has meta minimum threshold or failed to meet a maximum threshold in a mannersimilar to that described in connection with the FIG. 3 bias evaluators530, 540. The outputs of bias evaluators 230 and 240 are input to acontrol 201.

A second parallel system for use in the MIMO transceiver is also shownin FIG. 6. In particular, a buffer 215 holds the characteristics ofanother received signal within a window based on input 298, with thewindow size of buffer 215 being adjustable in response to a signal 251.The values stored in the buffer 215 are again output as an in-phase andquadrature-phase signal that are input to a bias detector 225 thatdetects a bias as noted above. Once the bias has been detected, the biasvalue is output to the bias evaluators 235 and 245.

The bias evaluators 235 and 245 again determine whether or not the biashas met a minimum threshold or failed to meet a maximum threshold or iswithin allowable transmission signal values as noted above with biasevaluators 530, 540 of FIG. 3. The outputs of bias evaluators 235 and245 are also input to the control 201.

The control 201 thus receives the carrier leakage detection signal fromcircuits 230, 235, 240, 245 together with a signal detection signal(!sigDet) and optionally a sensitivity level signal (LEAK_DET_ANT_AND),such as shown in FIG. 7 described below. The signal detection signal(!sigDet) goes high when the receiver has received a CCA signal. So whenthe carrier leakage signal is high and there is a valid CCA signalreceived such that the carrier leakage signal (!sigDet) is high, thecontrol 201 will combine these signals logically and output a leakagedetection signal (leakDetEff) accordingly based on the sensitivity levelsignal LEAK_DET_ANT_AND (if employed).

FIG. 7 shows a more detailed embodiment of the circuit for detectingcarrier leakage shown in FIG. 6, including a sensitivity selector. Thelogical states such as the polarities of an input 299 of thetransmission frame 100 are stored in a buffer 210, such as a short syncbuffer, as ones (or alternatively zeros). The buffer 210 holds thepolarities of the received transmission frame 100 within a limited timewindow that is associated with a particular sampling rate. The length ofthe window being based on input 250. The values stored in the buffer 210are output as an in-phase (I) signal and a quadrature-phase (Q) signalthat are input to a counter 220. The counter 220 counts the number ofones that are input from the buffer 210 from the in-phase andquadrature-phase inputs within a given time-period. Once the number ofones has been counted in counter 220, the counter 220 outputs the numberof ones respectively to comparator circuits 230 and 240. Additionally,it is contemplated that multiple counters can be used to count thenumber of ones that are input from the buffer 210 from the in-phase andquadrature-phase inputs.

The I and Q phases are 90 degrees offset from one another. The 90-degreeseparation allows for two distinct windows in which to count ones orzeros. However, it is contemplated that a single-phase system could beused, however it may not be as robust as the I and Q phases but mayrequire less circuit or chip area.

In a specific embodiment shown in FIG. 7, the buffer 210 may hold thepolarities of the received signal within a 1.6 microsecond window. Thisis associated with a 40 MHz sampling rate. Accordingly, there are 64such stored polarities within the 1.6 microsecond window.

In one particular embodiment, if the number of ones exceeds the maximumthreshold (SS_leak_TH) or is less than window-size minus the maximumthreshold (for example, less than 64 minus the maximum thresholdSS_leak_TH (minimum threshold)), a signal indicating carrier leakage isoutput from comparator circuit 230 or circuit 240. In other words, thebasis for comparison is whether the number of ones is within allowabletransmission signal values indicative of a data transmission. Theoutputs of comparator circuit 230 and comparator circuit 240 are inputto an OR gate 250 in control circuit 201. The OR gate 250 outputs thecarrier leakage detection signal (leakDet_(—)1) when the carrier leakagedetection signal is received from either the comparator circuit 230 orthe comparator circuit 240. Thereafter the OR gate 250 inputs thecarrier leakage detection signal (leakDet_(—)1) to both an AND gate 260and an OR gate 265.

A second parallel system for use in the MIMO transceiver is also shownin FIG. 7. In particular, a buffer 215, such as a short sync buffer,holds the polarities of another received signal within a window based oninput 298. The values stored in the buffer 215 are again output as anin-phase and quadrature-phase signal that are input to a counter 225that counts the number of ones that are input from the buffer 215 fromthe in-phase and quadrature-phase inputs within a given time-periodwindow based on input 251. Once the number of ones has been counted inthe counter 225, this counter outputs the number of ones respectively tocomparator circuits 235 and 245.

The comparator circuits 235 and 245 determine whether or not the numberof ones has met a minimum threshold or failed to meet a maximumthreshold or are within allowable transmission signal values. Inparticular, if the number of ones exceeds the maximum threshold(SS_leak_TH) or is less than a window size minus the maximum threshold(for example, 64 minus the maximum threshold SS_leak_TH (minimumthreshold)), a signal indicating carrier leakage is set and output fromcomparator circuit 235 and/or circuit 245. The outputs of comparatorcircuit 235 and comparator circuit 245 are input to an OR gate 255 incontrol circuit 201. The OR gate 255 outputs the carrier leakagedetection signal (leakDet_(—)2) when the carrier leakage detectionsignal is received from either the comparator circuit 235 or thecomparator circuit 245. Thereafter, the OR gate 255 also outputs thecarrier leakage detection signal (leakDet_(—)2) to both the AND gate 260and the OR gate 265 that form a logical combination of the signals(leakDet_(—)1, leakDet_(—)2).

The output of both the AND gate 260 and the OR gate 265 is input to amultiplexer 270. The choice of whether the carrier leakage detectionsignal from the AND gate 260 or the carrier leakage detection signalfrom the OR gate 265 is selected is based on the selection signal(LEAK_DET_ANT_AND) the multiplexer 270 receives to select either the ANDgate 260 or the OR gate 265 outputs. The choice of the AND gate 260 orthe OR gate 265 input is a matter of sensitivity preference. Morespecifically, the sensitivity of determining whether the carrier leakage110 is detected is higher with the OR gate 265 than the AND gate 260. Inother words, the AND gate 260 requires at least one leak detectionsignal from each input 298, 299, whereas the OR gate 265 requires onlyone.

When the multiplexer 270 receives the carrier leakage detection signalon a channel that has been selected by the selection signal, themultiplexer 270 outputs the carrier leakage detection signal whencarrier leakage has been detected by that channel. This output is inputto an AND gate 280. The AND gate 280 ANDs the carrier leakage detectionsignal together with a signal detection signal (!sigDet). The signaldetection signal goes high when the receiver has received a valid clearchannel assessment (CCA) signal. So when the carrier leakage signal ishigh and there is a valid CCA signal received such that the carrierleakage signal (!sigDet) is high, the AND gate 280 outputs a leakagedetection signal (leakDetEff).

FIG. 8 shows a circuit for the detection of carrier leakage similar tothe FIG. 7 circuit, but without a sensitivity selector in the controlcircuit 401. The logical states, such as polarities of an input 499, arestored in a buffer 410, such as a short sync buffer, as ones (oralternatively zeros). The buffer 410 holds the polarities of thereceived signal within a limited time window that is associated with aparticular sampling rate or based on an input 450. The values stored inthe buffer 410 are output as an in-phase and quadrature-phase signalthat is input to a counter 420. The counter 420 counts the number ofones or zeros that are input from the buffer 410 from the in-phase andquadrature-phase inputs within a given time-period. Once the number ofones has been counted in counter 420, the counter 420 outputs the number(ctr I, ctr Q) of ones to comparator circuits 430 and 440, respectively.

In a specific embodiment shown in FIG. 8, the buffer 410 may hold thepolarities of the received signal within a 1.6 microsecond window. Thisis associated with a 40 MHz sampling rate. Accordingly there are 64 suchstored polarities within the 1.6 microsecond window.

The comparator circuits 430 and 440 determine whether or not the numberof ones and the number of zeros has met a minimum threshold or failed tomeet a maximum threshold (i.e. is within allowable values of goodtransmission). In one particular embodiment, if the number of onesexceeds the maximum threshold (SS_leak_TH) or is less than window sizeminus the maximum threshold (for example, 64 minus the maximum thresholdSS_leak_TH (minimum threshold)), a carrier leakage signal is set andoutput from comparator circuit 430 and/or circuit 440. The outputs ofcomparator circuit 430 and comparator circuit 440 are input to an ORgate 450 in control 401. The OR gate 450 outputs the carrier leakagedetection signal (leakDet_(—)1) when the carrier leakage detectionsignal is received from either the comparator circuit 430 or thecomparator circuit 440. Thereafter the OR gate 450 inputs the carrierleakage detection signal (leakDet_(—)1) to an AND gate 460.

A second parallel system for use in the MIMO transceiver is also shownin FIG. 8. In particular, a buffer 415, such as a short sync buffer,holds the polarities of another received signal 498 within a window oftime based on input 451. The values stored in the buffer 415 are againoutput as an in-phase and quadrature-phase signal that are input to acounter 425 that counts the number of ones that are input from thebuffer 415 from the in-phase and quadrature-phase outputs. Once thenumber of ones has been counted in counter 425, this counter outputs thenumber ones (ctrOneI, ctrOneQ) respectively to comparator circuits 435and 445.

The comparator circuits 435 and 445 again determine whether or not thenumber of ones and the number of zeros has met a threshold or is withinallowable transmission values. In one particular embodiment, when thenumber of ones exceeds the maximum threshold (SS_leak_TH) or is lessthan a window size minus the maximum threshold (SS_leak_TH (minimumthreshold)), a carrier leakage signal is set and output from comparatorcircuit 435 and/or comparator circuit 445 in control 401. The outputs ofcomparator circuit 435 and comparator circuit 445 are input to an ORgate 455. The OR gate 455 outputs the carrier leakage detection signal(leakDet_(—)2) when the carrier leakage detection signal is receivedfrom either the comparator circuit 435 or the comparator circuit 445.

The output of the both the OR gate 450 (leakDet_(—)1) and the OR gate455 (leakDet_(—)2) inputs to an AND gate 460. The output of AND gate 460inputs to an AND gate 480 that ANDs the carrier leakage detection signaltogether with a signal detection signal (!sigDet). The signal detectionsignal (!sigDet) goes high when the receiver has received a valid CCAsignal. So when the carrier leakage signal is high and the valid CCAsignal is high (!sigDet), the AND gate 480 outputs a leakage detectionsignal (leakDetEff). This output may then be used in conjunction withthe FIG. 9 circuit or alternatively without the FIG. 9 circuit describedbelow to avoid receiving transmission errors. Additionally, an OR gatemay be substituted for the AND gate 460 for increased sensitivity.

FIG. 9 shows a circuit for use with any of the leakage detection signalcircuits of the invention that is responsive to a protocol type signalto output a protocol signal when there is no carrier leakage or disablea protocol signal when there is carrier leakage. In particular, circuit300 shown in FIG. 9 receives, from AND gate 280 or control 501 forexample, the leakage detection signal (leakDetEff) in both an AND gate310 and an AND gate 320. Also being input to the AND gate 310 is a cs11bsignal, which is indicative of a CCA signal from the receiver indicatingreception of a particular WLAN transmission protocol type, such as forexample one that is compliant with IEEE 802.11, 802.11(a), 802.11(b),802.11(g), 802.11(n), 802.16, or 802.20. Similarly, the AND gate 320receives the leakage detection signal together with a CCA signal, suchas a cs11ng signal indicating reception of a different particular WLANtransmission protocol type, for example one that is compliant with IEEE802.11, 802.11(a), 802.11(b), 802.11(g), 802.11(n), 802.16, or 802.20.Accordingly, an absence of an output from the AND gate 310 of a cs11b′signal disables the erroneous reception of the carrier leakage 110 forthat transmission type; and the absence of an output from the AND gate320 of a cs11ng′ signal disables the erroneous reception of the carrierleakage 110 for that transmission type. Moreover, it is contemplatedthat the leakage detection signal also may reset the gain acquisitioncontrol circuitry, other similar circuitry, or system state in atransmitter to ensure transmission reception.

FIG. 10 shows an exemplary logic flow chart of a process for detectingcarrier leakage according the principles of the invention, which may beimplemented in the circuits of the invention. As shown in step S1000, awireless signal, such as a WLAN transmission frame 100, is received in areceiver. Next in step S1002, bias in a characteristic of the receivedwireless signal such as logical state is detected in accordance with theprinciples of the invention discussed above. The bias value of thesignal that is detected is output in step S1004.

As further shown in step S1006 of FIG. 10, it is determined whether ornot the bias is outside allowable transmission values. In particular,when the bias is outside the allowable transmission values, then thereis most likely some carrier leakage in the wireless signal. Morespecifically, the bias is outside the allowable transmission values whenthe bias has failed to meet a minimum threshold and/or exceeded amaximum threshold. When it is determined that the bias value is outsidean allowable transmission value the logic will flow to step S1008 alongthe Yes branch of the flow chart of FIG. 10. In step S1008, a signalindicating carrier leakage is output. The signal indicating carrierleakage subsequently may be logically combined with other receiversignals to disable the receiver to avoid a reception error and reducedthroughput caused by carrier leakage. On the other hand, should the biasvalue be inside an allowable transmission value, the logic will flow tothe No branch. Accordingly, the process of detecting carrier leakage maybe repeated for further received wireless signals.

It should be noted that although the counters are described in theabove-noted embodiments as counting ones it is contemplated that thecounters could also count zeros, changes in states or transitions, orany other logical states known in the art.

In accordance with various embodiments of the invention, the methodsdescribed herein are intended for operation with dedicated hardwareimplementations including, but not limited to, semiconductors,application specific integrated circuits, programmable logic arrays, andother hardware devices constructed to implement the methods and modulesdescribed herein. Moreover, various embodiments of the inventiondescribed herein are intended for operation as software programs runningon a computer processor. Furthermore, alternative softwareimplementations including, but not limited to, distributed processing,component/object distributed processing, parallel processing, virtualmachine processing, any future enhancements, or any future protocol canalso be used to implement the methods described herein.

It should also be noted that the software implementations of theinvention as described herein are optionally stored on a tangiblestorage medium, such as: a magnetic medium such as a disk or tape; amagneto-optical or optical medium such as a disk; or a solid statemedium such as a memory card or other package that houses one or moreread-only (non-volatile) memories, random access memories, or otherre-writable (volatile) memories. A digital file attachment to email orother self-contained information archive or set of archives isconsidered a distribution medium equivalent to a tangible storagemedium. Accordingly, the invention is considered to include a tangiblestorage medium or distribution medium, as listed herein and includingart-recognized equivalents and successor media, in which the softwareimplementations herein are stored.

The invention can be implemented in a variety of devices, some of whichare described in more detail below. Referring now to FIG. 11, theinvention can be implemented in a set top box 1180. The invention mayimplement either or both signal processing and/or control circuits,which are generally identified in FIG. 11 at 1184, a WLAN interfaceand/or mass data storage of the set top box 1180. The set top box 1180receives signals from a source such as a broadband source and outputsstandard and/or high definition audio/video signals suitable for adisplay 1188 such as a television and/or monitor and/or other videoand/or audio output devices. The signal processing and/or controlcircuits 1184 and/or other circuits (not shown) of the set top box 1180may process data, perform coding and/or encryption, performcalculations, format data and/or perform any other set top box function.

The set top box 1180 may communicate with mass data storage 1190 thatstores data in a nonvolatile manner. The mass data storage 1190 mayinclude optical and/or magnetic storage devices for example hard diskdrives HDD and/or DVDs. The HDD may be a mini HDD that includes one ormore platters having a diameter that is smaller than approximately 1.8″.The set top box 1180 may be connected to memory 1194 such as RAM, ROM,low latency nonvolatile memory such as flash memory and/or othersuitable electronic data storage. The set top box 1180 also may supportconnections with a WLAN via a WLAN network interface 1196 constructedaccording the principles of the invention.

Referring now to FIG. 12, the invention can be implemented in a highdefinition television (HDTV) 1220. The invention may implement either orboth signal processing and/or control circuits, which are generallyidentified in FIG. 12 at 1222, a WLAN interface and/or mass data storageof the HDTV 1220. The HDTV 1220 receives HDTV input signals in either awired or wireless format and generates HDTV output signals for a display1226. In some implementations, signal processing circuit and/or controlcircuit 1222 and/or other circuits (not shown) of the HDTV 1220 mayprocess data, perform coding and/or encryption, perform calculations,format data and/or perform any other type of HDTV processing that may berequired.

The HDTV 1220 may communicate with mass data storage 1227 that storesdata in a nonvolatile manner such as optical and/or magnetic storagedevices. The HDD may be a mini HDD that includes one or more plattershaving a diameter that is smaller than approximately 1.8″. The HDTV 1220may be connected to memory 1228 such as RAM, ROM, low latencynonvolatile memory such as flash memory and/or other suitable electronicdata storage. The HDTV 1220 also may support connections with a WLAN viaa WLAN network interface 1229 constructed according the principles ofthe invention.

Referring now to FIG. 13, the invention can be implemented in a controlsystem of a vehicle 1330, a WLAN interface and/or mass data storage ofthe vehicle control system. In some implementations, the invention canbe implemented a powertrain control system 1332 that receives inputsfrom one or more sensors such as temperature sensors, pressure sensors,rotational sensors, airflow sensors and/or any other suitable sensorsand/or that generates one or more output control signals such as engineoperating parameters, transmission operating parameters, and/or othercontrol signals.

The invention may also be implemented in other control systems 1340 ofthe vehicle 1330. The control system 1340 may likewise receive signalsfrom input sensors 1342 and/or output control signals to one or moreoutput devices 1344. In some implementations, the control system 1340may be part of an anti-lock braking system (ABS), a navigation system, atelematics system, a vehicle telematics system, a lane departure system,an adaptive cruise control system, a vehicle entertainment system suchas a stereo, DVD, compact disc and the like. Still other implementationsare contemplated.

The powertrain control system 1332 may communicate with mass datastorage 1346 that stores data in a nonvolatile manner. The mass datastorage 1346 may include optical and/or magnetic storage devices forexample hard disk drives HDD and/or DVDs. The HDD may be a mini HDD thatincludes one or more platters having a diameter that is smaller thanapproximately 1.8″. The powertrain control system 1332 may be connectedto memory 1347 such as RAM, ROM, low latency nonvolatile memory such asflash memory and/or other suitable electronic data storage. Thepowertrain control system 1332 also may support connections with a WLANvia a WLAN network interface 1348 constructed according the principlesof the invention. The control system 1340 may also include mass datastorage, memory and/or a WLAN interface (all not shown).

Referring now to FIG. 14, the invention can be implemented in a cellularphone 1450 that may include a cellular antenna 1451. The invention mayimplement either or both signal processing and/or control circuits,which are generally identified in FIG. 14 at 1452, a WLAN interfaceand/or mass data storage of the cellular phone 1450. In someimplementations, the cellular phone 1450 includes a microphone 1456, anaudio output 1458 such as a speaker and/or audio output jack, a display1460 and/or an input device 1462 such as a keypad, pointing device,voice actuation and/or other input device. The signal processing and/orcontrol circuits 1452 and/or other circuits (not shown) in the cellularphone 1450 may process data, perform coding and/or encryption, performcalculations, format data and/or perform other cellular phone functions.

The cellular phone 1450 may communicate with mass data storage 1464 thatstores data in a nonvolatile manner such as optical and/or magneticstorage devices for example hard disk drives HDD and/or DVDs. The HDDmay be a mini HDD that includes one or more platters having a diameterthat is smaller than approximately 1.8″. The cellular phone 1450 may beconnected to memory 1466 such as RAM, ROM, low latency nonvolatilememory such as flash memory and/or other suitable electronic datastorage. The cellular phone 1450 also may support connections with aWLAN via a WLAN network interface 1468 constructed according theprinciples of the invention.

Referring now to FIG. 15, the invention can be implemented in a mediaplayer 1500. The invention may implement either or both signalprocessing and/or control circuits, which are generally identified inFIG. 15 at 1504, a WLAN interface and/or mass data storage of the mediaplayer 1500. In some implementations, the media player 1500 includes adisplay 1507 and/or a user input 1508 such as a keypad, touchpad and thelike. In some implementations, the media player 1500 may employ agraphical user interface (GUI) that typically employs menus, drop downmenus, icons and/or a point-and-click interface via the display 1507and/or user input 1508. The media player 1500 further includes an audiooutput 1509 such as a speaker and/or audio output jack. The signalprocessing and/or control circuits 1504 and/or other circuits (notshown) of the media player 1500 may process data, perform coding and/orencryption, perform calculations, format data and/or perform any othermedia player function.

The media player 1500 may communicate with mass data storage 1510 thatstores data such as compressed audio and/or video content in anonvolatile manner. In some implementations, the compressed audio filesinclude files that are compliant with MP3 format or other suitablecompressed audio and/or video formats. The mass data storage may includeoptical and/or magnetic storage devices for example hard disk drives HDDand/or DVDs. The HDD may be a mini HDD that includes one or moreplatters having a diameter that is smaller than approximately 1.8″. Themedia player 1500 may be connected to memory 1514 such as RAM, ROM, lowlatency nonvolatile memory such as flash memory and/or other suitableelectronic data storage. The media player 1500 also may supportconnections with a WLAN via a WLAN network interface 1516 constructedaccording the principles of the invention. Still other implementationsin addition to those described above are contemplated.

While the invention has been described in terms of exemplaryembodiments, those skilled in the art will recognize that the inventioncan be practiced with modifications in the spirit and scope of theappended claims. These examples given above are merely illustrative andare not meant to be an exhaustive list of all possible designs,embodiments, applications or modifications of the invention.

What is claimed:
 1. An apparatus, comprising: a measurement circuitconfigured to generate a measurement signal indicative of a bias in asignal received via a communication channel; and a circuit configured togenerate, using the measurement signal, a detection signal thatindicates presence of an unmodulated radio frequency (RF) carrier priorto a communication frame in the signal received via the communicationchannel.
 2. An apparatus according to claim 1, further comprising abuffer to store logical states corresponding to the signal received viathe communication channel, wherein the measurement circuit is configuredto generate the measurement signal based on logical states stored in thebuffer.
 3. An apparatus according to claim 1, wherein the measurementcircuit is configured to: count a number of transitions between logicalstates corresponding to the signal received via the communicationchannel; and generate the measurement signal based on the number oftransitions.
 4. An apparatus according to claim 1, wherein themeasurement circuit is configured to: determine a time period of aparticular logical state in the signal received via the communicationchannel; and generate the measurement signal based on the time period.5. An apparatus according to claim 1, wherein: the measurement circuitincludes a counter configured to count a number of values thatcorrespond to a particular logical state in the signal received via thecommunication channel; and the measurement circuit is configured togenerate the measurement signal based on the number of values thatcorrespond to the particular logical state.
 6. An apparatus according toclaim 5, wherein: the circuit configured to generate the detectionsignal includes a comparator to compare the measurement signal to athreshold; and the circuit is configured to generate the detectionsignal based on an output of the comparator.
 7. An apparatus accordingto claim 1, wherein: the measurement circuit includes i) a first counterconfigured to count a number of values that correspond to a particularlogical state in an in-phase component of the signal received via thecommunication channel, and ii) a second counter configured to count anumber of values that correspond to the particular logical state in aquadrature component of the signal received via the communicationchannel; the measurement signal is a first measurement signal; themeasurement circuit is configured to i) generate the first measurementsignal based on the number of values that correspond to the particularlogical state in the in-phase component, and ii) generate a secondmeasurement signal based on the number of values that correspond to theparticular logical state in the quadrature component; the circuitconfigured to generate the detection signal includes i) a firstcomparator to compare the first measurement signal to a threshold, andii) a second comparator to compare the second measurement signal to thethreshold; and the circuit is configured to generate the detectionsignal based on i) an output of the first comparator, and ii) an outputof the second comparator.
 8. An apparatus according to claim 1, wherein:the measurement signal is a first measurement signal; the measurementcircuit is configured to i) generate the first measurement signal basedon an in-phase component of the signal received via the communicationchannel, and ii) generate a second measurement signal based on aquadrature component of the signal received via the communicationchannel; and the circuit configured to generate the detection signal isconfigured to generate the detection signal using the first measurementsignal and the second measurement signal.
 9. An apparatus according toclaim 1, further comprising a further circuit configured to generate,using i) the detection signal and ii) a first protocol detection signalindicative of detection of a frame conforming to a first communicationprotocol, a frame detect signal indicative of detection of acommunication frame.
 10. An apparatus according to claim 9, wherein thefurther circuit is configured to generate the frame detect signalfurther using a second protocol detection signal indicative of detectionof a frame conforming to a second communication protocol.
 11. Anapparatus of claim 1, wherein the measurement signal indicative of thebias is indicative of a particular bias in favor of one of a pluralityof possible logical states.
 12. A method, comprising: generating ameasurement signal indicative of a bias in a signal received via acommunication channel; and generating, using the measurement signal, adetection signal that indicates presence of an unmodulated radiofrequency (RF) carrier prior to a communication frame in the signalreceived via the communication channel.
 13. A method according to claim12, further comprising storing, in a buffer, logical statescorresponding to the signal received via the communication channel,wherein generating the measurement signal is based on logical statesstored in the buffer.
 14. A method according to claim 12, whereingenerating the measurement signal comprises: counting a number oftransitions between logical states corresponding to the signal receivedvia the communication channel; and generating the measurement signalbased on the number of transitions.
 15. A method according to claim 12,wherein generating the measurement signal comprises: determining a timeperiod of a particular logical state in the signal received via thecommunication channel; and generating the measurement signal based onthe time period.
 16. A method according to claim 12, wherein generatingthe measurement signal comprises: counting a number of values thatcorrespond to a particular logical state in the signal received via thecommunication channel; and generating the measurement signal based onthe number of values that correspond to the particular logical state.17. A method according to claim 16, wherein generating the detectionsignal comprises: comparing the measurement signal to a threshold; andgenerating the detection signal based on whether the measurement signalmeets the threshold.
 18. A method according to claim 12, wherein: themeasurement signal is a first measurement signal; wherein generating thefirst measurement signal comprises counting a number of values thatcorrespond to a particular logical state in an in-phase component of thesignal received via the communication channel, and generating the firstmeasurement signal based on the number of values that correspond to theparticular logical state in the in-phase component; wherein the methodfurther comprises counting a number of values that correspond to theparticular logical state in a quadrature component of the signalreceived via the communication channel, and generating a secondmeasurement signal based on the number of values that correspond to theparticular logical state in the quadrature component; and whereingenerating the detection signal comprises comparing the firstmeasurement signal to a threshold, comparing the second measurementsignal to the threshold, and generating the detection signal based on i)whether the first measurement signal meets the threshold, and ii)whether the second measurement signal meets the threshold.
 19. A methodaccording to claim 12, wherein: the measurement signal is a firstmeasurement signal; generating the first measurement signal comprisesgenerating the first measurement signal based on an in-phase componentof the signal received via the communication channel; the method furthercomprises generating a second measurement signal based on a quadraturecomponent of the signal received via the communication channel, whereingenerating the detection signal comprises using the first measurementsignal and the second measurement signal.
 20. A method according toclaim 12, further comprising generating, using i) the detection signaland ii) a first protocol detection signal indicative of detection of aframe conforming to a first communication protocol, a frame detectsignal indicative of detection of a communication frame.
 21. A methodaccording to claim 20, wherein generating the frame detect signalfurther comprises using a second protocol detection signal indicative ofdetection of a frame conforming to a second communication protocol. 22.A method according to claim 12, further comprising disabling a receiverwhen the detection signal indicates presence of the unmodulated RFcarrier prior to a communication frame in the signal received via thecommunication channel.
 23. A method according to claim 12, furthercomprising resetting a gain control circuit when the detection signalindicates presence of the unmodulated RF carrier prior to acommunication frame in the signal received via the communicationchannel.
 24. A method according to claim 12, further comprisingresetting a system state in a transmitter when the detection signalindicates presence of the unmodulated RF carrier prior to acommunication frame in the signal received via the communicationchannel.
 25. A method according to claim 12, wherein generating themeasurement signal comprises determining whether the received signal hasa particular bias in favor of one of a plurality of possible logicalstates.